CIHM 

ICMH 

Microfiche 

Collection  de 

Series 

microfiches 

(l\/lonograplis) 

(monographles) 

Canadian  Institut*  for  Historical  Microraproductioni  /  inatitut  Canadian  do  microraproductiona  historiquaa 


Technical  and  Bibliographic  Notes  /  Notes  technique  et  bibliographiques 


The  Institute  has  attempted  to  obtain  the  tiest  original 
copy  available  for  filnning.  Features  of  this  copy  which 
may  be  bibliographically  unique,  which  may  alter  any  of 
the  images  in  the  reproduction,  or  which  may 
significantly  change  the  usual  method  of  filming  are 
checked  beiow. 

rV|     Coloured  covws/ 
' — '     Couverture  de  couleur 

I     I     Covers  damaged  / 

' — '     Couverture  endommagte 

I     I     Covers  restored  and/or  laminated  / 
' — '     Couverture  restaurte  et/ou  pellicula 

I     I     Cover  title  missing /Letltrede  couverture  manque 

I     I     Coloured  maps  /  Cartes  giographiques  en  couleur 

I     I     Cotoured  ink  (i.e.  other  than  blue  or  black)/ 
Encre  de  couleur  (i.e.  autre  que  Ueue  ou  noire) 

0|     Cokxired  plates  and/or  illustratky<s/ 

'—^        Planches  At/m  illiustrAtinnfi  nn  miilMiii 


D 
D 


D 


Planches  et/ou  Illustrations  en  couleur 

Bound  with  other  material  / 
ReliS  avec  dautres  documents 


Only  editk>n  available  / 
Seule  Mitkm  disponifale 

Tight  binding  may  cause  shadows  or  distortion 
along  Interior  margin  /  La  reliure  serree  peut 
causer  de  I'ombre  ou  de  la  distorsnn  le  k)ng  de 
la  marge  interieure. 

Blank  leaves  added  during  restoratkHis  may  appear 
within  the  text.  Whenever  possible,  these  have 
been  omitted  from  timing  /  II  so  peul  que  csrtaines 
pages  blanches  ajoutees  kxs  dune  restauratkm 
apparaissent  dans  le  texle,  mais,  kxsque  osia  ilail 
possible,  ces  pages  n'ont  pas  He  Umies. 


L'Institut  a  microfilm^  le  meilleur  examplaire  qu'il  lui  a 
6t6  possible  de  se  procurer.  Les  details  de  cet  exem- 
plaire  qui  sont  peut-4tre  uniques  du  point  de  vue  bibli- 
ographlque,  qui  peuvent  modifier  une  image  reproduite, 
ou  qui  peuvent  exiger  une  modifications  dans  la  m^th- 
ode  normale  de  filmage  sont  indiqu^s  ci-dessous. 

I     I     Cotoured  pages/ Pages  de  couleur 

I     I     Pages  damaged  /  Pages  endommagees 

I     I     Pages  restored  an*or  laminated  / 
' —      Pages  restaurees  et/ou  pellknjiees 

r^    Pages  discokHired,  stained  or  foxed  / 
' — '     Pages  dteotorees.  tachettes  ou  piqu^es 

I     I     Pages  detached/ Pages  detachees 

I  y/\      Showthrough  /  Transparence 

I     I     Quality  of  print  varies  / 

'— '      Qualiti  in^gale  de  I'impressnn 

I     I     Includes  supptomentaiy  material  / 
' —      CoinprenddumatMetsuppMmentBire 

I  I  Pages  wholly  or  partially  obscured  by  errata 
' — '  slips,  tissues,  etc.,  have  been  relilmed  to 
ensure  the  best  possible  image  /  Les  pages 
totalement  ou  partiellement  ot>scurcies  par  un 
feuillet  d'enata,  une  pelure,  etc.,  ont  ete  filmees 
i  nouveau  de  fa;on  a  obtenir  la  meilleure 
image  possll>le. 

I  I  Opposing  pages  with  varying  colouration  or 
' — '  discolourations  are  filmed  twice  to  ensure  the 
best  possible  image  /  Les  pages  s'opposant 
ayant  des  colorations  variables  ou  des  dicol- 
oratkins  sont  filmees  deux  fois  afin  d'obtenir  la 
meilleur  image  possible. 


izl 


AdiAkxial  comments  / 
Commentaiies  suppMmentaires: 


Pagination  Is  as  folio 


p.  [*].  818-823. 


This  imn  ii  tilmad  at  tiM  rsductian  ratio  diadiad  balow/ 

Cc  documant  ast  filmi  su  taux  da  rWvctTon  tndlqf#  ci-dessous. 

10X  14X  18X 


22X 


2(X 


/ 


1(X 


2ax 


Th*  copy  fllmtd  hara  hM  ba«n  raproduead  thanks 
to  tha  ganarotity  of: 

Blacker-Wood  Library  of  Biology 
McGIII  University,  Montreal 


L'axamplaira  tilmi  fut  raproduit  griea  i  la 
g4n*ro*it*  da: 

Blacker-Kood  Library  of  Biology 
McCni   University,  Montreal 


Tha  Imaga*  appaaring  hara  ara  tha  baat  quality 
poMlbIa  eontidaring  tha  condition  and  laglblllty 
of  tha  original  copy  and  In  kaaping  with  tha 
filming  contract  ipaclficatlons. 


La*  imagas  lulvantat  ont  ttt  raproduitat  ivac  la 
plua  grand  tain,  eompta  tanu  da  la  condition  at 
da  la  nattatt  da  Taxamplaira  film*,  at  en 
eonformltA  avac  lat  eondltlont  du  contrat  da 
fllmaga. 


Original  eoplaa  in  printad  papar  eovars  ara  fllmad 
baginning  with  tha  front  covar  and  anding  on 
tha  last  paga  with  a  printad  or  llluatratad  Impras- 
tion.  or  tha  back  covar  whan  approprlats.  All 
othar  original  eoplaa  ara  fllmad  baginning  on  tha 
f  irat  paga  with  a  printad  or  llluatratad  impraa- 
alon,  and  anding  on  tha  laat  paga  with  a  printad 
or  llluatratad  impraaaion. 


Laa  axamplalrat  triginaux  dont  la  couvartura  an 
paplar  aat  imprimta  lont  filmte  an  eommancant 
par  la  pramiar  plat  at  an  tarminant  toit  par  la 
darniira  paga  qui  comporta  una  amprtinta 
d'imprataion  ou  d'HIuttratlon,  toit  par  la  ttcond 
plat,  talon  la  eat.  Tout  lat  autrat  axamplairat 
orlginaux  tont  fllmto  an  commandant  par  la 
pramitra  paga  qui  comporta  una  amprainta 
d'Impraaaion  ou  d'HIuttratlon  at  an  tarminant  par 
la  darnitra  paga  qui  k.amporta  una  talla 
amprainta. 


Tha  laat  raeordad  frama  on  aach  mierofleha 
thall  conuin  tha  tymbol  — » (moaning  "CON- 
TINUED'I.  or  tha  tymbol  ▼  (maaning  "END"), 
whichavar  appliaa. 


Un  daa  tymboiat  tuivantt  ipparaltra  tur  la 
darnitra  imaga  da  chaqua  microfiche,  talon  la 
cat:  la  tymbola  —^  tignifia  "A  SUIVRE '.  la 
tymbola  ▼  tignifia  "FIN". 


Mapt,  plataa.  chartt.  ate.  may  bo  fllmad  at 
diffarant  raduction  ratiot,  Thota  too  larga  to  bo 
ontlraly  ineludad  in  ona  axpotura  ara  fllmad 
baginning  in  tha  uppar  laft  hand  comar.  laft  to 
right  and  top  to  bottom,  at  many  framat  aa 
raqulrad.  Tha  following  diagramt  illuatrata  tha 
mathod: 


Laa  cartaa,  planchat,  tableaux,  ate.  pauvant  itra 
tllmto  i  dat  taux  da  rMuction  diffaranit. 
Lortqua  la  document  att  trop  grand  pour  itra 
reproduit  en  un  teul  clicht,  il  ect  film*  i  partir 
da  I'angla  tup4riaur  gauche,  de  gauche  i  droitc. 
et  da  haut  an  bat.  en  pranant  le  nombre 
d'imagaa  ndcataaira.  Lee  diagrammat  tuivantt 
illuttrant  la  mtthoda. 


1 

2 

3 

1 

2 

3 

4 

5 

6 

Mietocorr  •■souition  ti«t  chait 

(ANSI  and  ISO  TEST  CHART  No.  2| 


1.0 


I.I 


■it 


170 


^  is 


/APPLIED   IM^SE     Inc 


1E53   Cost   Mom   Strael 
RochwlBf.   Htm   rork         i 
(716)   *e2  -0300- WiQfi 
(Tie)  288-8969 -Fa. 


Th£  E^-ES  OF  THE  BURROWING  OWL 

WITH  SPECIAL  MTERENCE  TO  THE  FUMDUt  OCUU 


■j^   WOOD,   M.D. 
Chicago.  III. 


REPRINTED  FROM 
>NTRIBUT10NS  TO  MKHCAL  AND  BIOLOGICAL  RBSBARCH, 
DEDICATED  TO  SIR  WILUAM  OSLBR,  IN  HONOUR  OF 
.  }JI8  SEYENJIBTH  BIRTHDAY,  JULY  I  J,  1919, 

iaii  •  ■''■■'-  ■  ■  ■  '-•  ' — ■-^-  ■— ^^ — ^ 


liR.  t  Asey  WOOD 

HUHrnrri  I'nlvaniir  P.  «.. 
<iilir»rnU 

THE  EYES  OF  THE  BURROWING  OWL 

WITH   SPECIAL   REFERENCE  TO   THE 
FUNDUS    OCULI 


BY 

CASEY  WOOD,   M.D. 

Chicago,  III. 


REPRINTED   FROM 

CONTRIBUTIONS  TO  MEDICAL  AND  BIOLOGICAL  RESEARCH, 

DEDICATED  TO  SIR  WILLIAM  OSLER,  IN  HONOUR  OF  HIS 

SEVENTIETH  BIRTHDAY,  JULY  12,  1919,  BY 

HIS  PUPILS  AND  CO-WORKERS. 


I 


THE  EYES  OF  THE  BURROWING  OWL 

WITH  SPECIAL   REFERENCE  TC  1ME   FUNDUS  OCULI 

By  Casky  a.  Wood,  M.D.,  Chicago.  III. 

OF  all  the  Strigiformes  there  is  none  so  interesting  from  the 
standpoint  of  the  visual  apparatus  as  that  widely  distrib- 
uted New  World  group— the  Burrowing  Owls.  These  birds 
are  found  (as  the  typical  species,  Sptotyto  cuniculnria)  through©  it 
the  oan-.piis  regions  of  Central  South  America  and  w.casionally  far- 
ther south;  and  are  well  known,  as  e  subspecies,  in  Florida  (Spiofyto 
c.  floridana),  the  West  J-idia  Islands,  and  on  the  plains  and  in  the 
valleys  of  North  America  (Sptotyto  c.  bypogga)  as  far  north  as 
British  Coliimbia. 

Of  the  numerous  subspecies  may  be  mentioned  also  the  small, 
pale-brown,  insectivorous,  Short-Winged  Burrowing  Owl  (Speotyto 
c.  bradyyttra)  inhabiting  th^  island  of  SanU  Margarita,  Venezuela; 
and  the  Haitian  form— 5p««yto  c.  dominicmsis.  The  Florida  Owl 
is  also  seen  in  the  Bahamas.  Although  smaller  than  the  typical 
spocies,  it  has  larger  feet  and  bill;  the  plumage  is,  on  the  whole, 
darker,  v.ith  clear  white  spots. 

All  Burrowing  Owls  are  comparatively  small  (less  th.n  1 1  inches 
in  length),  but  this  peculiarity  k  .lot  so  noticeable  on  account  of 
their  unusually  long,  bare  legs.  Their  h.ibits  are  said  to  be  mainly 
diurnal,  but  observations  of  the  North  American  species  by  the 
wr:ter  incline  him  t  the  belief  that  they  are  essentially  nocturnal 
animals,  like  most  owls.  Burrowing  habits  seem  to  be  common  to 
all  the  species,. 

Burrowing  owls  have  a  dull-brownish,  spotted,  and  barred 
1  nage;  the  middle  of  the  chest  is  white  and  is  partly  encircled  by 
a  plainly  marked  buff-brown  collar.  The  liead  is  rather  flat  and  small, 
the  facial  disks  are  not  well  defined,  the  bill  is  short,  and  the  wings 
are  relatively  undeveloped,  sc  the  bird  is  able  to  fly  only  short 
distances. 
\-T\^4\  8.8 


Big 


THE  EYES  OF  THE  BURROWING  OWL 


The  food  of  these  owls  consists  almost  entirely  of  mice,  gophers, 
and  similar  mammals,  as  well  as  of  small  reptiles  and  insects.  Of 
these  a  family  of  owls,  commonly  ten  in  number,  will  consume 
enormous  quantities;  each  member  disposing  of  his  own  weight 
of  pabulum  in  twenty-four  hours! 

According  to  Knowlton  and  Ridgway  (i)  the  Burrowing  Owl  is 
more  or  less  migratory,  and  after  a  return  to  its  usual  habitat  mates 
(probably  for  life)  and  then  arranges  its  underground  nest.  The 
contour  of  these  nesting  burrows  varies;  they  are  usually  about  15 
inches  wide  and  from  j  to  10  feet  in  length.  They  enter  the  ground 
in  a  diagonal  direction  for  a  few  feet  and  then  turn  at  an  angle  either 
to  the  right  or  to  the  left.  The  nesting  chamber  (la  to  18  inches  in 
width),  placed  at  the  highest  part  of  the  burrow,  is  mostly  lined 
with  dry  dung,  but  sometimes  with  hair,  feathers,  or  dried  grass. 
The  eggs  are  six  to  twelve  (generally  eight)  in  number;  their 
color,  when  unsoiled,  is  glossy  white. 

It  must  be  remembered  that  while  the  great  majority  of  these 
owls  dig  their  own  burrows,  many  of  them,  especially  the  northern 
varieties,  make  use  of  the  abandoned  holes  of  certain  mammals, 
notably  of  the  prairie  dog,  fox,  badge>,  '  jnk,  and  ground  squirrel. 
Doubtless  in  the  latter  instances  the  Burrowing  Owl  may  enlarge 
or  otherwise  alter  the  size,  length,  and  othei  dimensions  of  the  newly 
acquired  hole. 

The  Burrowing  Owi  is  not  over-clean  in  his  habits;  the  nesting 
chamber  and  the  remainder  of  the  burrow  are  often  filthy  and  foul 
smelling. 

The  writer  has  studied  the  habits  of  the  North  American  and 
Florida  subspecies,  with  special  attention  to  the  eyes  and  eyesight 
of  the  bird.  From  these  observations  he  concludes  that  this  owl, 
like  all  the  others,  is  a  true  night  bird,  adapting  itself  with  but  slight 
success  to  daylight  conditions.  In  spite  of  the  fact  that  Bendire  and 
Hudson  refer  to  the  animal  as  a  diurnal  owl,  their  accounts  of  its 
habits  really  bear  out  the  writer's  contention  of  a  nocturnal  animal 
with  fairly  good  ('ly  vision,  yet  distinctly  embarrassed,  uncertain, 
and  confused  when  the  eyes  are  exposed  to  bright  sunlight.  Stress 
is  laid  by  a  number  of  observers  upon  the  fact  that  this  owl  is  seen 
at  all  times  of  the  day  standing  guard,  often  on  a  little  mound  of 
earth  in  front  of  his  burrow  entrance,  forgetting  that,  as  a  much 


Th*  Fundus  OcuU  of  the  Burrowing  Owl-.S>„(„(„  cumculurh  hijiM^mt. 


! 


THE  EYES  OF  THE  BURROWING  OWL 


820 

of  t^!  ,W  T''  °^  ^  'f ''"  ^"'^"^'^^  ^*"''y  °f  the  visual  apparatus 
him  that  the  bird  ever  performs  an  act  requirinR  distinct  dZ.7j 
vision.  Certainly  the  northern  bird  is  decidedly  noctj  nXoct  on 
ally  using  h.s  eyes,  but  at  a  disadvantage,  during  daylight  hou   ? 

This  conclusion  ,s  confirmed  in  a  noteworthy  fashion  by  a  com 
pa  .son  of  the  fundus  oculi  of  this  owl  with  the  same  pLure  Tn 
owls  entirely  nocturnal  in  their  habits,  and  indeed  with  certa  n 
other  evidence  (especially  that  they  all  show  orange  or  redS 
fundi)  constantly  found  in  night  animals. 

These  facts  have  been  fully  stated  by  G.  Lindsay  Johnson  (2) 
as  regards   he  mammalia;  and  by  the  writer  (3)  for  the  alTeye 

As  m  all  owls,  the  eyeballs  are  set  well  in  front  and  surrounded 

S^St:Z:u^-  '-"  '''  -  °^  '■>«  '•^'^-dtn^d 
Stngiform  eyes  more  closely  than  those  of  any  other  order  r, 

reWon  toXrT'  T'  ''''  "T"^'  ^^  '"  -"-'^-  "h-amj 
^InTn  LI^  ^/     !  °ir  r'' "'  ^°  P'''^"'  ^^  to  obtain  binocular 
vision  .n/ron«  Structurally,  of  course,  birds'  eyes  are  quite  different 
especially  in  the  morphology  of  the  eyeball,  in'^the  possession  by  the 
owl  of  a  pecten  instead  of  retinal  vessels,  in  the  coCed  optic  neve 

sLTt"''  M  "  Tr^"""  "^'^  '"  "  "°t  proper  to  spedfy  her? 

Slonaker  (4    and  the  writer  (5)  have  pointed  out  that  all  rh^ 

owls  are  exceptions  to  the  rule  that  the  retinal  area  0?^  " sL„ 


Sai 


THE  EYES  OF  THE  BURROWING  OWL 


is  in  birds  with  a  single  fovea  placed  above  and  towards  the  nasal 
aspect  of  the  optic  nerve  entrance.  The  owls  possess  a  single,  deep 
fovea  encircled  by  a  round,  sharply  defined  area  located  above 
and  on  the  temporal  side  of  the  optic  disk.  This  arrangement  closely 
approaches  the  binocular  macule  of  man. 

The  writer  gives  to  the  owls  a  class  by  itself  in  describing  these 
ares  and  affirms  that  the  temporal  monomacular  fundus  is  found 
almost  exclusively  in  the  owls. 

In  conjunction  with  Arthur  W.  Head,  F.  Z.  S.,  the  South  Ameri- 
can Burrowing  Owls  in  the  London  Zoological  Gardens  were  closely 
studied  and  examined  with  the  ophthalmoscope.  In  addition,  the 
interior  of  the  eyeball     , 
both  of  that  type  and 
ofseveral  North  Amer- 
ican individuals  were 
examined  by  the  writer 
in  prepared  specimens. 

The  ophthalmo- 
scope in  particular 
shows  the  fundus  oculi 
of  Speolyto  cuntcu/ario 
to  be  that  of  a  typical 
nocturnal  animal.  The 
picture  of  this  bird's 
background  is  well  shown  in  the  accompanying  colored  plate, 
painted  by  Head  and  faithfully  reproduced  here.  The  ocular 
fundus  of  this  species  is  irregularly  round,  as  in  all  the  owls,  and 
in  prepared  specimens  these  details  show  distinctly. 

The  single,  temporal,  oval  macular  region  lies  above  and  about 
a  disk  length  and  a  half  from  the  upper  end  of  the  papilla.  In  the 
center  of  the  macula  is  the  fovea— a  dark  pigmented  spot  with  fine 
granules  arranged  cap-like  above  it.  Outside  this,  again,  is  the  ovoid 
circumference  of  this  region,  incompletely  edged  with  fine  dots. 
These  are  more  numerously  distributed  below  the  macula  than 
above  it.  Connected  with  the  macular  region  is  a  light-colored  and 
rather  broad  band  that  extends  horizontally  to  the  center  of  the 
visible  background.  It  is  unevenly  divided  into  two  strips  by  a 
parallel  arrangement  of  minute  pigment  dots. 


Lateral  View  of  the  Pecten  of  the  Burrowing  Owl- 
Speolyto  cuniculana  bypogxa.    x  9- 


THE  EYES  OF  THE  BURROWING  OWL 


822 


Seen  from  above,  the  relatively  small  perten  closely  resembles  a 
disarticulated,  acuminate  leaf,  the  stem  representing  the  spinous 
projection  immediately  above  the  lowest  terminal  convolution.  The 
light  double  folds  of  the  marsupium  slope  backwards  and  cover  most 
of  the  optic  entrance;  they  meet  above  in  a  uniform,  very  narrow, 
slightly  undulating  crest  whose  posterior  end  projects  half  the  height 
of  the  underlying  coil  well  into  the  vitreous  cavity.  An  extension 
upwards  of  the  long  axis  of  the  disk  cuts  the  retinal  band  at  the 
junction  of  the  inner  and  second  fourth,  making  an  infulapapillary 
angle  of,  perhaps,  40°. 

This  interesting  owl  is  especially  subject,  like  other  Strigiformes, 
to  pathological  variations  in  the  fundus  picture  after  confinement 
and  domestication.  Both  Head  and  the  writer  examined  a  number 
of  individuals  that  undoubtedly  exhibited  choroidal  disease  and 
other  pathological  changes.  Rejecting  these,  the  general  color  of 
the  fundus  of  this  species  is  found  to  be  dull-orange,  mottled  and 
blotched  in  its  upper  half  with  deep  orange-red.  Choroidal  vessels 
are  plainly  visible,  covering  all  the  lower  part  of  the  eyeground,  just 
as  in  the  Tawny  Owl.  The  well-defined  macular  area  is  seen  within 
the  outer  half  of  the  fundus,  a  little  above  the  upper  extremity  of 
the  optic  disk.  It  is  distinguished  from  the  surrounding  choroid  by 
a  collection  of  minute  pigment  granules  or  dots  with  a  bright,  white 
spot  in  their  center. 

The  optic  disk  is  white  and  of  oblong  shape,  slightly  rounded  at 
the  ends.  From  its  edges  run  a  few  short  nerve  fibers  that  form  a 
complete  fringe  about  the  visible  papilla. 

The  pecten  is  decidedly  larger  in  proportion  to  bodily  measure- 
ments than  one  finds  it  in  most  of  the  larger  owls,  especially  larger 
than  in  the  Tawny  Owl.  It  extends  well  forward  into  the  vitreous, 
and  its  lower  half  appears  very  massive  and  of  a  dark  brown  color. 
The  pectinate  convolutions  are  plainly  seen  and  the  anterior  or 
upper  half  is  more  delicate  in  structure,  being  perforated  where  it 
joins  the  disk.  Here  it  forms  a  dark  network  on  the  surface  of  the 
nervehead,  where,  also,  a  few  red  granules  mingle  with  the  chocolate- 
brown  texture  of  the  pecten. 


8a3  THE  EYES  OF  THE  BURROWING  OWL 

BIBLIOGRAPHY 

I.  "Birds  of  the  World,"  p.  537. 
1.  Phil.  Tr.,  Lond.,  1901. 

3.  "Fundus  Oculi  of  Birds,"  Chicago,  1917. 

4.  Jr.  Morpb.,  1897,  XIII,  44;. 

5.  Am.  Encyc.  Opbtb.,  1914,  IV,  2JI9. 


Paul  B.  Hoebek,  67-69-71  East  sgrH  Stkeet,  New  York. 


